Synchronous hybrid automatic repeat request (HARQ) protocol employing a first information element indicating whether to perform retransmission of an uplink data packet and a second information element indicates modulation and coding scheme (MCS) for the retransmission

ABSTRACT

A base station receives an uplink data packet from a user equipment based on a synchronous hybrid automatic repeat request (HARQ) protocol, and transmits a first information element and a second information element in parallel to the user equipment. The first information element indicates whether to perform a retransmission of the uplink data packet, and the second information element indicates modulation and coding scheme (MCS) for the retransmission. The base station receives the retransmission from the user equipment according to the modulation and coding scheme. The first information element is for example an ACK/NACK feedback message.

CROSS-REFERENCE TO RELATED APPLICATIONS

This is a continuation application of application Ser. No. 12/835,696(now U.S. Pat. No. 7,979,770) filed Jul. 13, 2010, which is acontinuation application of application Ser. No. 10/594,496 (now U.S.Pat. No. 7,783,949) filed Aug. 7, 2007, which is a national stage ofPCT/EP2005/002561 filed Mar. 10, 2005, which is based on EuropeanApplication No. 04008017.8 filed Apr. 1, 2004, the entire contents ofeach of which are incorporated by reference herein.

FIELD OF THE INVENTION

The present invention relates to a method for controlling the amount ofinformation in retransmission data packets transmitted from atransmitting entity to a receiving entity via at least one data channelusing a hybrid automatic repeat request protocol. Further, the presentinvention provides a receiving entity and a transmission entity bothadapted to perform the respective method steps. Moreover, acommunication system is provided which comprises at least one receivingentity and at least one receiving entity.

TECHNICAL BACKGROUND

W-CDMA (Wideband Code Division Multiple Access) is a radio interface forIMT-2000 (International Mobile Communication), which was standardizedfor use as the 3^(rd) generation wireless mobile telecommunicationsystem. It provides a variety of services such as voice services andmultimedia mobile communication services in a flexible and efficientway. The standardization bodies in Japan, Europe, USA, and othercountries have jointly organized a project called the 3^(rd) GenerationPartnership Project (3GPP) to produce common radio interfacespecifications for W-CDMA.

The standardized European version of IMT-2000 is commonly called UMTS(Universal Mobile Telecommunication System). The first release of thespecification of UMTS has been published in 1999 (Release 99). In themean time several improvements to the standard have been standardized bythe 3GPP in Release 4 and Release 5 and discussion on furtherimprovements is ongoing under the scope of Release 6.

The dedicated channel (DCH) for downlink and uplink and the downlinkshared channel (DSCH) have been defined in Release 99 and Release 4. Inthe following years, the developers recognized that for providingmultimedia services—or data services in general—high speed asymmetricaccess had to be implemented. In Release 5 the high-speed downlinkpacket access (HSDPA) was introduced. The new high-speed downlink sharedchannel (HS-DSCH) provides downlink high-speed access to the user fromthe UMTS Radio Access Network (RAN) to the communication terminals,called user equipments in the UMTS specifications.

Hybrid ARQ Schemes

The most common technique for error detection of non-real time servicesis based on Automatic Repeat reQuest (ARQ) schemes, which are combinedwith Forward Error Correction (FEC), called Hybrid ARQ. If CyclicRedundancy Check (CRC) detects an error, the receiver requests thetransmitter to send additional bits or a new data packet. From differentexisting schemes the stop-and-wait (SAW) and selective-repeat (SR)continuous ARQ are most often used in mobile communication.

A data unit will be encoded before transmission. Depending on the bitsthat are retransmitted three various types of ARQ may be defined.

In HARQ Type I the erroneous data packets received, also called PDUs(Packet Data Unit) are discarded and new copy of that PDU isretransmitted and decoded separately. There is no combining of earlierand later versions of that PDU. Using HARQ Type H the erroneous PDU thatneeds to be retransmitted is not discarded, but is combined with someincremental redundancy bits provided by the transmitter for subsequentdecoding. Retransmitted PDU sometimes have higher coding rates and arecombined at the receiver with the stored values. That means that onlylittle redundancy is added in each retransmission.

Finally, HARQ Type III is almost the same packet retransmission schemeas Type II and only differs in that every retransmitted PDU isself-decodable. This implies that the PDU is decodable without thecombination with previous PD Us. In case some PDUs are heavily damagedsuch that almost no information is reusable self decodable packets canbe advantageously used.

When employing chase-combining the retransmission packets carryidentical symbols. In this case the multiple received packets arecombined either by a symbol-by-symbol or by a bit-by-bit basis (see D.Chase: “Code combining: A maximum-likelihood decoding approach forcombining an arbitrary number of noisy packets”, IEEE Transactions onCommunications, Col. COM-33, pages 385 to 393, May 1985, incorporatedherein by reference). These combined values are stored in the softbuffers of respective HARQ processes.

Packet Scheduling

Packet scheduling may be a radio resource management algorithm used forallocating transmission opportunities and transmission formats to theusers admitted to a shared medium. Scheduling may be used in packetbased mobile radio networks in combination with adaptive modulation andcoding to maximize throughput/capacity by e.g. allocating transmissionopportunities to the users in favorable channel conditions. The packetdata service in UMTS may be applicable for the interactive andbackground traffic classes, though it may also be used for streamingservices. Traffic belonging to the interactive and background classes istreated as non real time (NRT) traffic and is controlled by the packetscheduler. The packet scheduling methodologies can be characterized by:

-   -   Scheduling period/frequency: The period over which users are        scheduled ahead in time.    -   Serve order: The order in which users are served, e.g. random        order (round robin) or according to channel quality (C/I or        throughput based).    -   Allocation method: The criterion for allocating resources, e.g.        same data amount or same power/code/time resources for all        queued users per allocation interval.

The packet scheduler for uplink is distributed between Radio NetworkController (RNC) and user equipment in 3GPP UMTS R99/R4/R5. On theuplink, the air interface resource to be shared by various users is thetotal received power at a Node B, and consequently the task of thescheduler is to allocate the power among the user equipment(s). Incurrent UMTS R99/R4/R5 specifications the RNC controls the maximumrate/power a user equipment is allowed to transmit during uplinktransmission by allocating a set of various transport formats(modulation scheme, code rate, etc.) to each user equipment. Theestablishment and reconfiguration of such a TFCS (transport formatcombination set) may be accomplished using Radio Resource Control (RRC)messaging between RNC and user equipment. The user equipment is allowedto autonomously choose among the allocated transport format combinationsbased on its own status e.g. available power and buffer status. Incurrent UMTS R99/R4/R5 specifications there is no control on timeimposed on the uplink user equipment transmissions. The scheduler maye.g. operate on transmission time interval basis.

UMTS Architecture

The high level R99/4/5 architecture of Universal MobileTelecommunication System (UMTS) is shown in FIG. 1 (see 3GPP TR 25.401:“UTRAN Overall Description”, incorporated herein by reference). Thenetwork elements are functionally grouped into the Core Network (CN)101, the UMTS Terrestrial Radio Access Network (UTRAN) 102 and the UserEquipment (UE) 103. The UTRAN 102 is responsible for handling allradio-related functionality, while the CN 101 is responsible for routingcalls and data connections to external networks. The interconnections ofthese network elements are defined by open interfaces (Iu, Uu). Itshould be noted that UMTS system is modular and it is therefore possibleto have several network elements of the same type.

FIG. 2 illustrates the current architecture of UTRAN. A number of RadioNetwork Controllers (RNCs) 201, 202 are connected to the CN 101. EachRNC 201, 202 controls one or several base stations (Node Bs) 203, 204,205, 206, which in turn communicate with the user equipments. An RNCcontrolling several base stations is called Controlling RNC (C-RNC) forthese base stations. A set of controlled base stations accompanied bytheir C-RNC is referred to as Radio Network Subsystem (RNS) 207, 208.For each connection between User Equipment and the UTRAN, one RNS is theServing RNS (S-RNS). It maintains the so-called Iu connection with theCore Network (CN) 101. When required, the Drift RNS 302 (D-RNS) 302supports the Serving RNS (S-RNS) 301 by providing radio resources asshown in FIG. 3. Respective RNCs are called Serving RNC (S-RNC) andDrift RNC (D-RNC). It is also possible and often the case that C-RNC andD-RNC are identical and therefore abbreviations S-RNC or RNC are used.

Enhanced Uplink Dedicated Channel (E-DCH)

Uplink enhancements for Dedicated Transport Channels (DTCH) arecurrently studied by the 3GPP Technical Specification Group RAN (see3GPP TR 25.896: “Feasibility Study for Enhanced Uplink for UTRA FDD(Release 6)”, incorporated herein by reference). Since the use ofIP-based services become more important, there is an increasing demandto improve the coverage and throughput of the RAN as well as to reducethe delay of the uplink dedicated transport channels. Streaming,interactive and background services could benefit from this enhanceduplink.

One enhancement is the usage of adaptive modulation and coding schemes(AMC) in connection with Node B controlled scheduling, thus anenhancement of the Un interface. In the existing R99/R4/R5 system theuplink maximum data rate control resides in the RNC. By relocating thescheduler in the Node B the latency introduced due to signaling on theinterface between RNC and Node B may be reduced and thus the schedulermay be able to respond faster to temporal changes in the uplink load.This may reduce the overall latency in communications of the userequipment with the RAN. Therefore Node B controlled scheduling iscapable of better controlling the uplink interference and smoothing thenoise rise variance by allocating higher data rates quickly when theuplink load decreases and respectively by restricting the uplink datarates when the uplink load increases. The coverage and cell throughputmay be improved by a better control of the uplink interference.

Another technique, which may be considered to reduce the delay on theuplink, is introducing a shorter TTI (Transmission Time Interval) lengthfor the E-DCH compared to other transport channels. A transmission timeinterval length of 2 ms is currently investigated for use on the E-DCH,while a transmission time interval of 10 ms is commonly used on theother channels. Hybrid ARQ, which was one of the key technologies inHSDPA, is also considered for the enhanced uplink dedicated channel. TheHybrid ARQ protocol between a Node B and a user equipment allows forrapid retransmissions of erroneously received data units, and may thusreduce the number of RLC (Radio Link Control) retransmissions and theassociated delays. This may improve the quality of service experiencedby the end user.

To support enhancements described above, a new MAC sub-layer isintroduced which will be called MAC-eu in the following (see 3GPP TSGRAN WG1, meeting #31, Tdoc R01-030284, “Scheduled and Autonomous ModeOperation for the Enhanced Uplink”). The entities of this new sub-layer,which will be described in more detail in the following sections, may belocated in user equipment and Node B. On user equipment side, the MAC-euperforms the new task of multiplexing upper layer data (e.g. MAC-d) datainto the new enhanced transport channels and operating HARQ protocoltransmitting entities.

E-DCH MAC Architecture at the User Equipment

FIG. 4 shows the exemplary overall E-DCH MAC architecture on userequipment side. A new MAC functional entity, the MAC-eu 503, is added tothe MAC architecture of Rel/99/4/5. The E-DCH MAC architecture includesRLC and higher layer entities 501, a MAC-d entity 502, the newfunctional entity MAC-eu 503, and the Physical Layer 504. The MAC-eu 503entity is depicted in more detail, in FIG. 5.

There are M various data flows (MAC-d) carrying data packets to betransmitted from user equipment to Node B. These data flows can havedifferent QoS (Quality of Service), e.g. delay and error requirements,and may require different configurations of HARQ instances. Thereforethe data packets can be stored in different Priority Queues. The set ofHARQ transmitting and receiving entities, located in user equipment andNode B respectively will be referred to as HARQ process. The schedulerwill consider QoS parameters in allocating HARQ processes to differentpriority queues. MAC-eu entity receives scheduling information from NodeB (network side) via Layer 1 signaling.

E-DCH MAC Architecture at the UTRAN

In soft handover operation the MAC-eu entities in the E-DCH MACArchitecture at the UTRAN side may be distributed across Node B(MAC-cub) and S-RNC (MAC-cur). The scheduler in Node B chooses theactive users and performs rate control by determining and signaling acommanded rate, suggested rate or TFC (Transport Format Combination)threshold that limits the active user (UE) to a subset of the TCFS(Transport Format Combination Set) allowed for transmission.

Every MAC-eu entity corresponds to a user (UE). In FIG. 6 the Node BMAC-eu architecture is depicted in more detail. It can be noted thateach HARQ Receiver entity is assigned certain amount or area of the softbuffer memory for combining the bits of the packets from outstandingretransmissions. Once a packet is received successfully, it is forwardedto the reordering buffer providing the in-sequence delivery to upperlayer. According to the depicted implementation, the reordering bufferresides in S-RNC during soft handover (see 3GPP TSG RAN WG 1, meeting#31: “HARQ Structure”, Tdoc R1-030247, incorporated herein byreference). In FIG. 7 the S-RNC MAC-eu architecture which comprises thereordering buffer of the corresponding user (UE) is shown. The number ofreordering buffers is equal to the number of data flows in thecorresponding MAC-eu entity on user equipment side. Data and controlinformation is sent from all Node Bs within Active Set to S-RNC duringsoft handover.

It should be noted that the required soft buffer size depends on theused HARQ scheme, e.g. an HARQ scheme using incremental redundancy (IR)requires more soft buffer than one with chase combining (CC).

E-DCH Signaling

E-DCH associated control signaling required for the operation of aparticular scheme consists of uplink and downlink signaling. Thesignaling depends on uplink enhancements being considered.

In order to enable Node B controlled scheduling (e.g. Node B controlledtime and rate scheduling), user equipment has to send some requestmessage on the uplink for transmitting data to the Node B. The requestmessage may contain status information of a user equipment e.g. bufferstatus, power status, channel quality estimate. The request message isin the following referred to as Scheduling Information (SI). Based onthis information a Node B can estimate the noise rise and schedule theUE. With a grant message sent in the downlink from the Node B to the UE,the Node B assigns the UE the TFCS with maximum data rate and the timeinterval, the UE is allowed to send. The grant message is in thefollowing referred to as Scheduling Assignment (SA).

In the uplink user equipment has to signal Node B with a rate indicatormessage information that is necessary to decode the transmitted packetscorrectly, e.g. transport block size (TBS), modulation and coding scheme(MCS) level, etc. Furthermore, in case HARQ is used, the user equipmenthas to signal HARQ related control information (e.g. Hybrid ARQ processnumber, HARQ sequence number referred to as New Data Indicator (NDI) forUMTS Rel. 5, Redundancy version (RV), Rate matching parameters etc.)

After reception and decoding of transmitted packets on enhanced uplinkdedicated channel (E-DCH) the Node B has to inform the user equipment iftransmission was successful by respectively sending ACK/NAK in thedownlink.

Mobility Management within R99/4/5 UTRAN

In this section some frequently used terms will be briefly defined andsome procedures connected to mobility management will be outlined (see3GPP TR 21.905: “Vocabulary for 3GPP Specifications”, incorporatedherein by reference).

A radio link may be a logical association between single UE and a singleUTRAN access point. Its physical realization comprises radio bearertransmissions.

A handover may be defined as transfer of a user's connection from oneradio bearer to another. In contrast, during “soft handover” (SHO) radiolinks are established and abandoned such that the UE always keeps atleast one radio link to the UTRAN. Soft handover is specific fornetworks employing Code Division Multiple Access (CDMA) technology.Handover execution is commonly controlled by S-RNC in mobile radionetwork.

The “active set” comprises a set of radio links simultaneously involvedin a specific communication service between UE and radio network, e.g.during soft handover, the UE's active set comprises all radio links tothe RAN's Node Bs serving the UE.

An Active set update procedure modifies the active set of thecommunication between UE and UTRAN. The procedure comprises threefunctions: radio link addition, radio link removal and combined radiolink addition and removal. The maximum number of simultaneous radiolinks is set to eight. New radio links may be added to the active setonce the pilot signal strengths of respective base stations exceedcertain threshold relative to the pilot signal of the strongest memberwithin active set. A radio link may be removed from the active set oncethe pilot signal strength of the respective base station exceeds certainthreshold relative to the strongest member of the active set. Thethreshold for radio link addition is typically chosen to be higher thanthat for the radio link deletion.

Hence, addition and removal events form a hysteresis with respect topilot signal strengths. Pilot signal measurements are reported to thenetwork (S-RNC) from the UE by means of RRC signaling. Before sendingmeasurement results, some filtering my be performed to average out thefast fading. A typical filtering duration may be about 200 ms and theduration contributes to handover delay. Based on measurement results,S-RNC may decide to trigger the execution of one of the functions ofactive set update procedure.

E-DCH Node B Controlled Scheduling

Node B controlled scheduling is one of the technical features for E-DCHwhich is foreseen to enable more efficient use of the uplink powerresource in order to provide a higher cell throughput in the uplink andto increase the coverage. The term “Node B controlled scheduling”denotes the possibility for the Node B to control, within the limits setby the RNC, the set of TFCs from which the UE may choose a suitable TFC.The set of TFCs from which the UE may choose autonomously a TFC is inthe following referred to as “Node B controlled TFC subset”. “Node Bcontrolled TFC subset” is a subset of the TFCS configured by RNC as seenin FIG. 8. The UE selects a suitable TFC from the “Node B controlled TFCsubset” employing the Rel5 TFC selection algorithm. Any TFC in the “NodeB controlled TFC subset” might be selected by the UE, provided there issufficient power margin, sufficient data available and TFC is not in theblocked state. Two fundamental approaches to scheduling UE transmissionfor the E-DCH exist. The scheduling schemes can all be viewed asmanagement of the TFC selection in the UE and mainly differs in how theNode B can influence this process and the associated signalingrequirements.

Node B Controlled Rate Scheduling

The principle of this scheduling approach is to allow Node B to controland restrict the transport format combination selection of the userequipment by fast TFCS restriction control. A Node B may expand/reducethe “Node B controlled subset”, which user equipment can chooseautonomously on suitable transport format combination from, by Layer-1signaling. In Node B controlled rate scheduling all uplink transmissionsmay occur in parallel but at a rate low enough such that the noise risethreshold at the Node B is not exceeded. Hence, transmissions fromdifferent user equipments may overlap in time. With Rate scheduling aNode B can only restrict the uplink TFCS but does not have any controlof the time when UEs are transmitting data on the E-DCH. Due to Node Bbeing unaware of the number of UEs transmitting at the same time noprecise control of the uplink noise rise in the cell may be possible(see 3GPP TR 25.896: “Feasibility study for Enhanced Uplink for UTRA FDD(Release 6)”, version 1.0.0, incorporated herein by reference). Two newLayer-1 messages are introduced in order to enable the transport formatcombination control by Layer-1 signaling between the Node B and the userequipment. A Rate Request (RR) may be sent in the uplink by the userequipment to the Node B. With the RR the user equipment can request theNode B to expand/reduce the “Node controlled TFC Subset” by one step.Further, a Rate Grant (RG) may be sent in the downlink by the Node B tothe user equipment. Using the RG, the Node B may change the “Node Bcontrolled TFC Subset”, e.g. by sending up/down commands. The new “NodeB controlled TFC Subset” is valid until the next time it is updated.

Node B Controlled Rate and Time Scheduling

The basic principle of Node B controlled time and rate scheduling is toallow (theoretically only) a subset of the user equipments to transmitat a given time, such that the desired total noise rise at the Node B isnot exceeded. Instead of sending up/down commands to expand/reduce the“Node B controlled TFC Subset” by one step, a Node B may update thetransport format combination subset to any allowed value throughexplicit signaling, e.g. by sending a TFCS indicator (which could be apointer).

Furthermore, a Node B may set the start time and the validity period auser equipment is allowed to transmit. Updates of the “Node B controlledTFC Subsets” for different user equipments may be coordinated by thescheduler in order to avoid transmissions from multiple user equipmentsoverlapping in time to the extent possible. In the uplink of CDMAsystems, simultaneous transmissions always interfere with each other.Therefore by controlling the number of user equipments, transmittingsimultaneously data on the E-DCH, Node B may have more precise controlof the uplink interference level in the cell. The Node B scheduler maydecide which user equipments are allowed to transmit and thecorresponding TFCS indicator on a per transmission time interval (TTI)basis based on, for example, buffer status of the user equipment, powerstatus of the user equipment and available interference Rise overThermal (RoT) margin at the Node B.

Two new Layer-1 messages are introduced in order to support Node Bcontrolled time and rate scheduling. A Scheduling Information Update(SI) may be sent in the uplink by the user equipment to the Node B. Ifuser equipment finds a need for sending scheduling request to Node B(for example new data occurs in user equipment buffer), a user equipmentmay transmit required scheduling information. With this schedulinginformation the user equipment provides Node B information on itsstatus, for example its buffer occupancy and available transmit power.

A Scheduling assignment (SA) may be transmitted in the downlink from aNode B to a user equipment. Upon receiving the scheduling request theNode B may schedule a user equipment based on the scheduling information(SI) and parameters like available RoT margin at the Node B. In theScheduling Assignment (SA) the Node B may signal the TFCS indicator andsubsequent transmission start time and validity period to be used by theuser equipment.

Node B controlled time and rate scheduling provides a more precise RoTcontrol compared to the rate-only controlled scheduling as alreadymentioned before. However this more precise control of the interferenceat this Node B is obtained at the cost of more signaling overhead andscheduling delay (scheduling request and scheduling assignment messages)compared to rate control scheduling.

In FIG. 9 a general scheduling procedure with Node B controlled time andrate scheduling is shown. When a user equipment wants to be scheduledfor transmission of data on E-DCH it first sends a scheduling request toNode B. T_(prop) denotes here the propagation time on the air interface.The contents of this scheduling request are information (schedulinginformation) for example buffer status and power status of the userequipment. Upon receiving that scheduling request, the Node B mayprocess the obtained information and determine the schedulingassignment. The scheduling will require the processing timeT_(schedule).

The scheduling assignment, which comprises the TFCS indicator and thecorresponding transmission start time and validity period, may be thentransmitted in the downlink to the user equipment. After receiving thescheduling assignment the user equipment will start transmission onE-DCH in the assigned transmission time interval.

The use of either rate scheduling or time and rate scheduling may berestricted by the available power as the E-DCH will have to co-existwith a mix of other transmissions by the user equipments in the uplink.The co-existence of the different scheduling modes may provideflexibility in serving different traffic types. For example, trafficwith small amount of data and/or higher priority such as TCP ACK/NACKmay be sent using only a rate control mode with autonomous transmissionscompared to using time and rate-control scheduling. The former wouldinvolve lower latency and lower signaling overhead.

E-DCH—Hybrid ARQ

Node B controlled Hybrid ARQ may allow rapid retransmissions oferroneously received data packets. Fast retransmissions between a userequipment and a Node B may reduce the number of higher layerretransmissions and the associated delays, thus the quality perceived bythe end user may be improved.

A protocol structure with multiple stop-and-wait (SAW) Hybrid ARQprocesses can be used for E-DCH, similar to the scheme employed for thedownlink HS-DSCH in HSDPA, but with appropriate modifications motivatedby the differences between uplink and downlink (see 3GPP TR 25.896).

An N-channel. SAW scheme consists of N parallel HARQ process, eachprocess works as a stop-and-wait retransmission protocols, whichcorresponds to a selective repeat ARQ (SR) with window size 1. It isassumed that user equipment can only transmit data on a single HARQprocess each transmission time interval.

In FIG. 10 an example N-channel SAW protocol with N=3 HARQ processes isillustrated. A user equipment is transmitting data packet 1 on E-DCH onthe uplink to the Node B. The transmission is carried out on the firstHARQ process. After propagation delay of the air interface T_(prop) theNode B receives the packet and starts demodulating and decoding.Depending on whether the decoding was successful an ACK/NACK is sent inthe downlink to the user equipment.

In this example Node B sends an ACK after T_(NBprocess), which denotesthe time required for decoding and processing the received packet inNode B, to the user equipment. Based on the feedback on the downlink theuser equipment decides whether it resends the data packet or transmits anew data packet. The processing time available for the user equipmentbetween receiving the ACKnowledgement and transmitting the nexttransmission time interval in the same HARQ process is denotedT_(UEprocess).

In the example user equipment transmits data packet 4 upon receiving theACK. The round trip time (RTT) denotes the time between transmission ofa data packet in the uplink and sending a retransmission of that packetor a new data packet upon receiving the ACK/NACK feedback for thatpacket. To avoid idle periods due to lack of available HARQ processes,it is necessary that the number N of HARQ processes matches to the HARQround trip time (RTT).

Considering known and unknown transmission timing, it may bedistinguished between synchronous and asynchronous data transmission. Aretransmission protocol with asynchronous data transmission uses anexplicit signaling to identify a data block or the HARQ process, whereasin a protocol with synchronous data transmission, a data block or HARQprocess is identified based on the point of time a data block isreceived.

A UE may for example have to signal the HARQ process number explicitlyin a protocol with asynchronous data transmission in order to ensurecorrect soft combining of data packets in case of a retransmission. Theadvantage of a HARQ retransmission protocol with asynchronous datatransmission is the flexibility, which is given to the system. The NodeB scheduler may for example assign UEs a time period and HARQ processesfor the transmission of data on the E-DCH based on the interferencesituation in the cell and further parameters like priority or QoSparameters of the corresponding E-DCH service.

A retransmission protocol with asynchronous HARQ feedback informationuses sequence numbers (SN) or other explicit identification of thefeedback messages whereas protocols with synchronous HARQ feedbackinformation identifies the feedback messages based on the time when theyare received, as for example in HSDPA. Feedback may be sent on theHS-DPCCH after a certain time instant upon having received the HS-DSCH(see 3GPP TR 25.848: “Physical Layer Aspects of High Speed DownlinkPacket Access”, version 5.0.0, incorporated herein by reference).

As mentioned before a retransmission protocol with asynchronous datatransmission enables the Node B more scheduling flexibility. Thescheduling assignment can for example be based on the schedulinginformation sent from UE and the interference situation in the cell. Thedifferent scheduling approaches considering retransmissions have to betaken into account, in order to enable further control of the uplinkinterference by the Node B scheduler.

A retransmission protocol with asynchronous uplink but synchronousretransmissions may be one approach, which allows the scheduler morecontrol on the noise rise in the cell. The transmission of new datapackets on E-DCH is sent in an asynchronous manner in order to keep theadvantage of scheduling flexibility, though the retransmissions are sentafter a predefined time instant upon having received the NACK. Theadvantages of a retransmission protocol with synchronous retransmissionsmay also depend on the scheduling mode used.

In the rate controlled scheduling mode Node B is only controlling theTFCS and the UE can choose among an appropriate TFC for the uplinktransmissions. Node B has no control on the UEs transmission time. Thereis also no restriction on the retransmission timing for the UE.Employing a retransmission protocol with synchronous retransmissionsNode B exactly knows when the retransmissions are sent by UE, hence itcan reserve uplink resources, which enables Node B a more precisecontrol on the uplink interference in the cell. In a time and ratecontrolled scheduling mode Node B schedules the initial—as well as theretransmissions sent on the E-DCH. In case retransmissions are sent in asynchronous manner, Node B doesn't need to schedule the retransmissionsanymore, which reduces the signaling overhead and the processing timefor the scheduler in Node B significantly. The retransmission is sentT_(sync) after having received the NACK. UE doesn't have to monitor thegrant channel for a scheduling assignment (SA) for the retransmission.

Due to transmitting retransmissions a fixed time period after receivingthe NACK (T_(sync)), there are delay benefits on UE side. In caseretransmissions are also scheduled, Node B could assign transmissionresources to other UEs instead of scheduling the pendingretransmissions.

In multi-access communication systems, techniques to reduce mutualinterference between multiple users may be utilized, in order toincrease the capacity. By means of for example power control techniquesthe transmission power of each user may be limited to a certain valuethat is necessary to achieve a desired quality of service. This approachmay ensure that each user transmits only the power necessary, therebymaking only the smallest possible contribution to the total noise seenby other users.

In this respect the interference caused by retransmissions may be animportant issue. In order to improve the capacity and hence in order toincrease the coverage and throughput of a communication system, it maybe desirable to keep the uplink interference caused by retransmissionsas small as possible. Especially in interference critical situations,where a lot of transmissions are most likely received in error, it maybe desirable that the corresponding retransmissions do not increase theinterference level in the cell significantly.

For example in a UMTS environment using a HARQ retransmission protocolwith synchronous retransmissions, it may be desirable that theinterference in the cell is not significantly increased due to a hugenumber of retransmissions, since a Node B may not have control on theretransmission timing.

Furthermore employing a HARQ retransmission scheme may increase the datatransmission efficiency, i.e. throughput and system performance, in amobile communication system. The power used for retransmissions may forexample be reduced by using the information received from the previouslyerroneously data packet to decode the retransmitted data packet.

More specifically, the soft decisions from the previous corrupted datapacket may be soft combined with the retransmitted data packet.Therefore the energy per bit (EbNt) required for a successful decodingof the data packet may be reduced for the retransmission. However in aconventional HARQ scheme the transmitting entity upon receiving aretransmission request has no knowledge of the reception quality of thepreviously incorrectly received data packet and hence does not know whatretransmission power level is required for a successful decoding aftersoft combining.

For example when utilizing a HARQ retransmission scheme with IncrementalRedundancy (IR) the transmitting entity does not know how muchadditional information (redundancy) is required for a successfuldecoding. When the transmission power for the retransmission data packetis too low or the amount of redundancy is not sufficient, the decodingwill most probably fail. Hence, the delay is increased due to furtherrequired retransmissions. On the other hand if the retransmission poweris more than required for a successful decoding resources are wasted,which could have been allocated for other initial transmissions.

US 2003/0235160 A1 describes an adaptive gain adjustment for theretransmission power of retransmission. The document proposes aretransmission protocol, where initial transmissions are transmitted ata first power level and retransmission data packets are transmitted withreduced power. Power control by means of the gain for retransmissions isadapted by adjusting the traffic-pilot ratio in order to optimise theperformance. The adjustment of the traffic-pilot ratio is based onwhether or not the previous retransmission data packet was successfullydecoded by the base station.

SUMMARY OF THE INVENTION

According to one embodiment of the present invention, a method forcontrolling the amount of information in retransmission data packetstransmitted from a transmitting entity to a receiving entity via atleast one data channel using a hybrid automatic repeat request protocoland soft combining of received data is provided.

The method may comprise transmitting a data packet from the transmittingentity to the receiving entity and receiving a feedback message from thereceiving entity at the transmitting entity, wherein the feedbackmessage indicates whether the data packet has been successfully receivedby the receiving entity.

In case the feedback message indicates that the data packet has not beenreceived successfully, a control message may be received at thetransmitting entity for the unsuccessfully received data packet, whereinthe control message restricts the amount of information to be sent inthe retransmission data packet for the unsuccessfully received datapacket.

Further, a retransmission data packet may be transmitted from thetransmitting entity to the receiving entity comprising an amount ofinformation indicated in the control message. According to a furtherembodiment of the present invention the control message may indicate themaximum and minimum amount of information or a maximum amount ofinformation in the retransmission data packet. In a further embodiment,the information sent in the retransmission packet may comprisesystematic and parity bits.

In another embodiment of the present invention the transmission of therestricted amount of information may require a reduced transmissionpower compared to the transmission power used for the data packet.

According to another embodiment, the control message may be transmittedin parallel or delayed to the feedback message from the receiving entityto the transmitting entity.

In a further embodiment, the feedback message may be transmitted via anacknowledgment channel and the control message may be transmitted via ascheduling related control channel.

Another embodiment of the present invention encompasses the use ofsynchronous retransmissions. Therefore, the retransmission data packetmay be transmitted by the transmitting entity after a predetermined timespan upon having received the feedback message.

Further, the control message may be used to indicate not to transmit theretransmission data packet after a predetermined time span upon havingreceived the feedback message. I.e. according to this further embodimentof the present invention the provision of synchronous or asynchronousretransmissions may be controlled.

In another embodiment of the invention the control message may be a TFCcontrol message. For example when using UMTS Rel99/4/5, the message maybe a TFC control message, which lists the allowed transport formatindicators (TFIs) for the restricted transport channel, theretransmission is transmitted on. In a further variation of thisembodiment, the restricted TFCS may be only valid for the retransmissionof the data packet, where after the TFCS reverts to the situation priorto the retransmission.

Further, in an alternative embodiment of the present invention themethod may further comprise soft combining the retransmission datapacket and the transmitted data packet at the receiving entity at thereceiving entity to obtain a combined data packet. According to anotherembodiment, this combined data packet may be decoded at the receivingentity.

Thus, it may be for example desirable that the transmitted controlmessage indicates the retransmission data packet's amount of informationnecessary for successfully decoding of the combined data packet, whichis a another aspect of the present invention.

In another embodiment, the method may further comprise determining theamount of information for the retransmission data packet at thereceiving entity based on the reception quality of the data packet orthe combined data packet.

A further embodiment encompasses the additional step of transmitting thedata packet via a first data channel from the transmitting entity to thereceiving entity. In this embodiment, the retransmission data packet maybe transmitted via a second data channel from the transmitting entity tothe receiving entity.

According to another embodiment of the present invention thetransmission time interval of the first data channel is smaller than thetransmission time interval of the second data channel.

In another embodiment of the present invention the transmitted datapacket and the retransmission data packet are transmitted via at leastone dedicated transport channel. According to a further embodiment ofthe present invention, a receiving entity for receiving data packetsfrom a transmitting entity via at least one data channel using a hybridautomatic repeat request protocol and soft combining of received data isprovided. The receiving entity may comprise receiving unit for receivinga data packet from the transmitting entity and transmitting unit fortransmitting a feedback message to the transmitting entity, wherein thefeedback message indicates whether the data packet has been successfullyreceived by the receiving entity.

The transmitting unit may be further adapted to transmit a controlmessage to the transmitting entity for the unsuccessfully received datapacket in case the feedback message indicates that the data packet hasnot been received successfully, wherein the control message restrictsthe amount of information to be sent in a retransmission data packet forthe unsuccessfully transmitted data packet, and the receiving unit maybe adapted to receive a retransmission data packet from the transmittingentity comprising an amount of information indicated in the controlmessage.

In another embodiment of the present invention a receiving entity isprovided which may be adapted to perform the above-outlined method.

For example, the receiving entity may be a base station.

A further embodiment of the present invention provides a transmittingentity for transmitting data packets to a receiving entity via at leastone data channel using a hybrid automatic repeat request protocol andsoft combining of received data. According to this embodiment, thetransmitting entity may comprise transmitting unit for transmitting adata packet from the transmitting entity and receiving unit forreceiving a feedback message from the receiving entity, wherein thefeedback message indicates whether the data packet has been successfullyreceived by the receiving entity.

The receiving unit may adapted to receive a control message at thetransmitting entity for the unsuccessfully received data packet in casethe feedback message indicates that the data packet has not beenreceived successfully, wherein the control message restricts the amountof information in a retransmission data packet to be sent for theunsuccessfully received data packet, and the transmitting unit mayadapted to transmit a retransmission data packet to the receiving entitycomprising an amount of information indicated in the control message.

In another embodiment of the present invention a transmitting entity isprovided which may be adapted to perform the above-outlined method.

In an exemplary embodiment, the transmitting entity is a mobileterminal.

Moreover, another embodiment of the present invention provides a mobilecommunication system comprising at least one receiving entity and atleast one transmitting entity described above.

Another embodiment of the present invention relates to acomputer-readable medium for storing instructions that, when executed ona processor, cause the processor to control the amount of information inretransmission data packets transmitted from a transmitting entity to areceiving entity via at least one data channel using a hybrid automaticrepeat request protocol and soft combining of received data by receivinga data packet from the transmitting entity, and transmitting a feedbackmessage to the transmitting entity, wherein the feedback messageindicates whether the data packet has been successfully received by thereceiving entity.

In case the feedback message indicates that the data packet has not beenreceived successfully, the instructions may further cause the processorto control the amount of information in retransmission data packets bytransmitting a control message to the transmitting entity for theunsuccessfully received data packet, wherein the control messagerestricts the amount of information to be sent in a retransmission datapacket for the unsuccessfully transmitted data packet, and receiving aretransmission data packet from the transmitting entity comprising anamount of information indicated in said control message.

A further embodiment of the present invention relates to acomputer-readable medium for storing instructions that, when executed ona processor, cause the processor to control the amount of information inretransmission data packets transmitted from a transmitting entity to areceiving entity via at least one data channel using a hybrid automaticrepeat request protocol and soft combining of received data bytransmitting a data packet from the transmitting entity, and receiving afeedback message from the receiving entity, wherein the feedback messageindicates whether the data packet has been successfully received by thereceiving entity. In case the feedback message indicates that the datapacket has not been received successfully, the instructions may furthercause the processor to control the amount of information inretransmission data packets by receiving a control message to thetransmitting entity for the unsuccessfully received data packet, whereinthe control message restricts the amount of information in aretransmission data packet to be sent for the unsuccessfully receiveddata packet, and transmitting a retransmission data packet to thereceiving entity comprising an amount of information indicated in saidcontrol message. Moreover, in a further embodiment of the presentinvention, the processor may be caused to perform the above describedembodiments related to a method using respective instructions stored onthe storage medium.

BRIEF DESCRIPTION OF THE FIGURES

In the following the present invention is described in more detail inreference to the attached figures and drawings. Similar or correspondingdetails in the figures are marked with the same reference numerals.

FIG. 1 shows the high-level architecture of UMTS,

FIG. 2 shows the architecture of the UTRAN according to UMTS R99/4/5,

FIG. 3 shows a Drift and a Serving Radio Subsystem,

FIG. 4 shows the E-DCH MAC architecture at a user equipment,

FIG. 5 shows the MAC-eu architecture at a user equipment,

FIG. 6 shows the MAC-eu architecture at a Node B,

FIG. 7 shows the MAC-eu architecture at a RNC,

FIG. 8 shows transport format combination sets for Node B controlledscheduling,

FIG. 9 shows the operation of a time and rate controlled schedulingmode,

FIG. 10 shows a the operation of a 3-channel stop-and-wait HARQprotocol,

FIG. 11 shows a HARQ protocol with synchronous retransmissions and TFCSrestriction by Node B for the retransmissions according to oneembodiment of the present invention, and

FIG. 12 shows a flow chart of the interference control method accordingto an exemplary embodiment of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

The following paragraphs will describe various embodiments of thepresent invention. For exemplary purposes only, most of the embodimentsare outlined in relation to a UMTS communication system and theterminology used in the subsequent sections mainly relates to the UMTSterminology. However, the used terminology and the description of theembodiments with respect to an UMTS architecture is not intended tolimit the principles and ideas of the present inventions to suchsystems. Generally, the principles of the present invention may beapplicable to any kind of mobile communication systems, for example tocommunication systems based on the IMT-2000 framework.

As will become apparent one of the various aspects of the presentinvention relates to controlling the amount of information inretransmissions to a minimum level such that—e.g. after soft combiningan initial transmission with at least one retransmission—decoding of thetransmitted data becomes possible. As will be explained in greaterdetail below, controlling the amount of information in retransmissionsmay decrease the required transmission power for the retransmissionswhich may lead to a significant decrease of the interference on the airinterface caused by retransmissions.

Within this document the term “information” may for example refer tosystematic bits and parity bits of an error-correcting code (FEC) whenusing a HARQ protocol employing chase combining. If for example anincremental redundancy scheme is employed, the information may compriseparity bits only. It is noted that generally and depending on theemployed retransmission protocol the data transmitted in theretransmissions may comprise redundancy only, systematic bits only or acombination thereof.

In an exemplary embodiment of the present invention it may be assumedthat the initial transmission of a data packet is transmitted with ahigher priority in terms of power than retransmissions. In case thatinitial transmissions do not meet the typical block error rates (BLER)and are transmitted with very little power only, then the retransmissiontransmit power may be higher than the transmit power of the initialtransmissions.

However, uplink transmissions may be subject to fast power control, forexample when considering the case of E-DCH. Due to the fast powercontrol, the received SNR (signal to noise ratio) of a failedtransmission may be only slightly smaller than the target SIR, which isrequired for a successful decoding.

Therefore if a retransmission for a data packet is transmitted with thesame transmission power as the initial transmission of the data packetassociated thereto—e.g. in the case of chase combining—the combined SNRafter soft combining may exceed the required SNR significantly. So thetransmit power for retransmissions may be reduced without reducing theprobability of a successful decoding.

According to an embodiment of the present invention, a limitation of theuplink interference may be achieved for example by reducing the numberof bits transmitted in the retransmission data packet. The informationtransmitted in the retransmission packet may comprise systematic as wellas parity bits. In case a smaller amount of information than in theinitial transmission is transmitted in the retransmissions, less powermay be required to send the retransmissions. Consequently, less uplinkinterference may be caused.

However, when the number of bits (information), sent in theretransmission, is not sufficient for a successful decoding furtherretransmissions may be required, which may increase delay.

Considering the example of a UMTS communication system, one method tocontrol the amount of information transmitted in the retransmissions maybe controlling the transport format combination set (TFCS), from whichUE can select a transport format combination (TFC) for theretransmission. A Node B may restrict the Transport formats (TFs) of thetransport channel, the retransmissions are transmitted on, such thatless information than in the initial transmission may be transmitted inthe retransmission. This method may provide Node B with some control onthe amount of information and, as a result, provides control on theuplink interference caused by the retransmissions. However, the decreasein the uplink interference may imply additional control signaling.Furthermore UE may monitor a scheduling related downlink control channelin order to receive the control message restricting the amount ofinformation for the retransmissions.

The UE may either constantly monitor the scheduling related downlinkcontrol channel or alternatively, a negative feedback message mayindicate to the UE that a control message should be received apredetermined time span after receiving the negative feedback message.The later option may enable the UE to save power in case there is noneed to constantly monitor the scheduling related downlink controlchannel.

In FIG. 11 shows a HARQ protocol with synchronous retransmissions andTFCS restriction by Node B for the retransmissions according to oneembodiment of the present invention. It should be noted that propagationdelays of the different messages are not shown in the figure.

First the UE being the transmitting entity transmits a data packet tothe receiving entity, for example a Node B. The data packet may be aninitial transmission of data or a retransmission. If the decoding of areceived data packet has failed, Node B may transmit a NACK to thecorresponding UE. The decoding attempt of the data packet is illustratedby the processing time T_(NodeBprocess). A TFC control message may betransmitted on a control channel. As outlined above the transmission ofthe TFC control message may either be simultaneously to the NACK or maybe delayed.

This TEC control message may restrict the TFCS at the UE from which theUE may choose one transport format combination for the retransmission.The TFCS may for example be reduced by one step, e.g. using a Rate Downcommand, or by several steps, e.g. TFCS indicator.

For example upon elapse of a predetermined time period upon havingreceived the NACK T_(sync) the UE may retransmit a data packet, i.e.send a retransmission data packet to the Node B.

According to another embodiment of the present invention, Node B mayalso set the TFCS to zero in an extreme case. When using a synchronousretransmission mode, this may indicate to the UE not to transmit theretransmission at the synchronous timing.

Another embodiment of the present invention provides a variation of thepreviously described embodiments. According to this embodiment; Node Bmay set the TFCS according to the reception quality of the received datapackets. For example, when using a HARQ protocol with incrementalredundancy (IR), Node B may control the amount of redundancy in theretransmissions by TFCS restriction control.

If only little additional redundancy is required for a successfuldecoding after soft combining of the retransmission and previouslystored transmissions, then Node B may restrict the TFCS of the UE. NodeB may estimate the required additional redundancy for a successfuldecoding based on the reception quality of the already receivedtransmissions of a data packet, i.e. the initial transmission andretransmissions that have been already transmitted for the data packet.The already received transmissions of a data packet may for example besoft combined and the necessary redundancy may be determined based onthe combined data.

The reception quality may be for example measured based on the softdecisions output (log likelihood ratios) of the decoder. The loglikelihood ratio (LLR) of a bit is generally defined as the logarithm ofthe ratio of probabilities. Therefore it carries some information aboutthe reliability of the bit decision. The sign of the LLR represents thebit decision (for example ‘−’ equals 1 and ‘+’ equals 0). The absolutevalue of a LLR may represent the reliability of the bit decision. If thebit decision for example is not very confident, the absolute value ofthe LLR is very small. Furthermore the reception quality may for examplealso be measured using a received signal strength value, a signal tointerference ratio (SIR) or a combination of possible measurementparameters.

So far the embodiments outlined above discussed the case that Node B orthe receiving HARQ protocol entity restricts the maximum amount ofinformation (bits) provided in the retransmission. In case theadditional information transmitted in the retransmission is notsufficient for a successful decoding, further retransmissions may berequired which may hence lead to an increased delay.

Therefore, according to another embodiment of the present invention, itmay be useful if the receiving entity also signals to the transmittingentity the minimum amount of information, which may be transmitted inthe retransmission. Hence, the transmitting entity may decide forexample depending on the current transmission buffer status and theavailable transmit power, whether to transmit more than the indicatedminimum amount of information or not.

Depending on the accuracy of the estimation for the additionalinformation required for a successful decoding, the HARQ protocoloperation may be further optimized if the receiving entity (for exampleNode B) sets an upper as well as lower limit of the amount ofinformation for the retransmissions.

A further approach for reducing the uplink interference may be to use alonger transmission time interval (TTI) length for the retransmissions.Initial transmissions may be for example sent in a 2 ms TTI and theretransmissions in a 10 ms TTI. Considering again for exemplary purposesonly a UMTS communication system, one E-DCH may be configured with a 2ms TTI length and may be used for the initial transmissions and anotherE-DCH with 10 ms TTI length may be used for the transmission of theretransmission data packets.

This may reduce interference caused by retransmissions, since thespreading factor may be increased if retransmissions are transmittedwith a longer TTI. Hence less transmit power may be required due to ahigher processing gain and thus interference may be controlled.Furthermore a longer TTI may provides more time diversity which may alsoallow for a further decrease of the transmit power of retransmissiondata packets.

If the transmission power for retransmissions may be reduced, the savedpower may be allocated to other UEs (initial transmissions), which mayincrease the cell throughput in consequence.

FIG. 12 shows a flow chart of the interference control method accordingto an exemplary embodiment of the present invention. According to thisexemplary example, in a first step 1201, a transmitting entity, forexample a UE, transmits a data packet or (retransmission data packet) tothe receiving entity, for example a Node B. Upon receiving the datapacket in step 1202, the receiving entity may determine whether the datapacket has been successfully decoded or not in step 1203.

If the data packet has been successfully decoded, a positive feedbackmessage, such as an ACK may be sent to the transmitting entity in step1204. Otherwise, a negative feedback, such as a NACK, may be transmittedto the transmitting entity in step 1205. Essentially in parallel to thenegative feedback or delayed thereto a further control message which mayrestrict the amount of information in a retransmission for theunsuccessfully received data packet may be provided to the transmittingentity in step 1206. When considering for exemplary purposes only a UMTSsystem, a TFC control message may be used to restrict the TFCS of a UEsuch that the retransmission will comprise a reduced amount ofinformation.

In step 1208, the transmitting entity may receive the feedback from thereceiving entity, and may next determine which type of feedback has beenreceived for the data packet transmitted in step 1201. If a positivefeedback has been received, the transmitting entity may proceed and sendthe next data packet waiting in the queue (see step 1209).

In case a negative feedback has been received in step 1207, thetransmitting entity may receive the control message transmitted from thereceiving entity in step 1210.

In an alternative variation of this embodiment, this message may bereceived via a scheduling related control channel, while the feedbackmay have been received via an acknowledgement channel.

Further, it should be noted that though FIG. 12 indicates a specificsequence of steps 1207, 1208 and 1210 the reception of the controlmessage in step 1210 may also be performed in parallel to step 1207,i.e. before judging the type of feedback in step 1208. In the latterexemplary case, the scheduling related control channel via which thecontrol message is transmitted may be constantly monitored. This may befor example because other control information may need to be obtainedfrom this channel for data transmission and reception purposes, such asscheduling, rate control, etc.

Alternatively, as indicated in FIG. 12 the control message may also betransmitted delayed to the feedback message, to allow the transmittingentity to receive the feedback, to determine its type and to startmonitoring the control channel for the control message transmitted fromthe receiving entity.

As outlined above, the information in the control message received instep 1210 may be used in step 1211 to form a retransmission data packet,comprising an amount of information as indicated in the control message.Upon forming the retransmission data packet same may be transmitted tothe receiving entity in step 1212.

Further, feedback for the retransmitted data packet is provided in asimilar manner as described above with reference to blocks 1202 to 1207.In step 1203, the initially transmitted data packet may be soft combinedwith the retransmissions prior to decoding. The embodiments of thepresent invention described with reference to FIG. 12 may be understoodas a new improved 1-channel SAW HARQ protocol. The skilled person willrecognize that it may also be possible to use the method shown in FIG.12 in a N-channel HARQ protocol, wherein N processes as shown in FIG. 12are performed in parallel. Moreover, another embodiment of the presentinvention relates to the implementation of the above described variousembodiments using hardware and software. It is recognized that thevarious above mentioned methods as well as the various logical blocks,modules, circuits described above may be implemented or performed usingcomputing devices, as for example general purpose processors, digitalsignal processors (DSP), application specific integrated circuits(ASIC), field programmable gate arrays (FPGA) or other programmablelogic devices, etc. The various embodiments of the present invention mayalso be performed or embodied by a combination of these devices.

Further, the various embodiments of the present invention may also beimplemented by means of software modules which are executed by aprocessor or directly in hardware. Also a combination of softwaremodules and a hardware implementation may be possible. The softwaremodules may be stored on any kind of computer readable storage media,for example RAM, EPROM, EEPROM, flash memory, registers, hard disks,CD-ROM, DVD, etc.

It would be appreciated by a person skilled in the art that numerousvariations and/or modifications may be made to the present invention asshown in the specific embodiments without departing from the spirit orscope of the invention as broadly described. The present embodimentsare, therefore, to be considered in all respects to be illustrative andnot restrictive.

What is claimed is:
 1. A method comprising the following steps performedby a base station: receiving an uplink data packet from a user equipmentbased on a synchronous hybrid automatic repeat request (HARQ) protocol,transmitting a first information element and a second informationelement in parallel to the user equipment, wherein the first informationelement indicates whether to perform a retransmission of the uplink datapacket, and the second information element indicates modulation andcoding scheme (MCS) for the retransmission, and receiving theretransmission from the user equipment according to the modulation andcoding scheme.
 2. The method according to claim 1, wherein the firstinformation element is an ACK/NACK feedback message.
 3. A base stationcomprising: a receiver section that receives an uplink data packet froma user equipment based on a synchronous hybrid automatic repeat request(HARQ) protocol, and, a transmitter section that transmits a firstinformation element and a second information element in parallel to theuser equipment, wherein the first information element indicates whetherto perform a retransmission of the uplink data packet, and the secondinformation element indicates modulation and coding scheme (MCS) for theretransmission, wherein the receiver section receives the retransmissionfrom the user equipment according to the modulation and coding scheme.4. The base station according to claim 3, wherein the first informationelement is an ACK/NACK feedback message.